The governor will make the announcement at noon at the State House in Columbia. She began informing the roster of finalists on Monday morning about her decision to go with Mr. Scott, who was the preferred candidate of many conservative leaders and groups in Washington.

Speaking on condition of anonymity, three Republican officials familiar with the process confirmed to The New York Times the decision to select Mr. Scott. Aides to the governor declined to comment before the noon announcement.

Ms. Haley seriously considered a number of potential contenders, particularly Jenny Sanford, the ex-wife of former Gov. Mark Sanford, who had been supportive of Ms. Haley in her race two years ago. But in choosing Mr. Scott, she selected a senator with a strong conservative voting record during his two years in Congress.